In the domain of tool-holder devices, and more particularly milling heads, two types of devices having a rotatable spindle-holder exist. According to the first type of device, angular positioning of the spindle-holder may be effected in a range of angular variation of 360.degree., but is necessarily equal to a given angle, for example 1.degree., 1.degree.15', 1.degree. 30', etc.. or a multiple of this angle. This is due to the fact that the tool-holder is blocked in position with respect to the body of the tool-holder device, via two crown gears, which mesh in one another, one being fixed on the body of the device, the other being fixed on the spindle-holder. Angular positioning of the spindle-holder is effected in a first step by slightly offsetting the spindle-holder in the direction of its axis of rotation so as to place the two crown gears out of engagement, then, in a second step, setting the spindle-holder thus released by a predetermined angle in rotation, and finally, in a third step, returning the spindle-holder into a position of blockage, in which the two crown gears mesh in one another. It will be understood that the relative positioning of the spindle-holder with respect to the body of the tool-holder device may be effected only by an incremental rotation corresponding at minimum to one tooth of the crown gears. The minimum angular positioning is therefore a function of the number of teeth of the two crown gears.
This first type of tool-holder device has for example already been described in German Patent Application published under No. DE 36 30260. The spindle-holder of the device described in this document possesses a double incremental rotation, in two perpendicular axes. It may therefore be adjusted in rotation in each of its two directions, but for each of these directions, the angular positioning is a function of the number of teeth of the coupling crown gears.
According to the second type of device, angular positioning of the spindle-holder is obtained along any angle by a continuous rotation of the spindle-holder. Japanese Patent Application of the firm TOSHIBA, published under number JP 59 182 037, describes a machine-tool head which, in manner similar to the device of document DE 36 30260, comprises a spindle-holder possessing a double rotation, along two perpendicular axes, but for which the means for setting in rotation along each axis allow a continuous angular adjustment of the spindle-holder.
Applicants' object is to propose a tool-holder device which is of the first type mentioned above, i.e. a tool-holder device allowing an incremental angular positioning of its spindle-holder, but which overcomes the principal drawback thereof by allowing an angular positioning of this spindle-holder by any angle between 0.degree. and 360.degree..